After you become a Junior member member this restriction becomes less strict. Search about the forum rules and you will realize how this works.
After the first two weeks, in which the user gained the available 14 activity, the restriction is reduced, and those members (although still nrwbies) are able to post faster than the 360seconds limit, and except they're spamming the forum they won't notice the little time restriction.
OP is probably, not an error, either you miscounted, or other parameters like last activity is used.